Field of the Invention
The present invention has as object a process and an apparatus for manufacturing tyres. More particularly, the invention is intended for the process and equipment used for building the green tyre, to be subsequently subjected to a moulding and curing cycle for the obtainment of the final product.
Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure comprising at least one carcass ply having respectively opposite end flaps engaged with respective annular anchoring structures, normally termed “bead cores”, integrated in the zones generally identified with the name of “beads”, having an internal diameter substantially corresponding to a so-called “fitting diameter” of the tyre on a respective mounting rim. In radially external position relative to the carcass structure, a belt structure is associated comprising one or more belt layers, situated in radial superimposition with respect to each other and with respect to the carcass ply, having textile or metallic reinforcement cords with cross orientation and/or substantially parallel to the circumferential extension direction of the tyre. In radially external position relative to the belt structure, a tread band is applied, also made of elastomeric material like other semi-finished products constituting the tyre. Between the tread band and the belt structure, a so-called “underlayer” can be interposed, made of elastomeric material with properties suitable for ensuring a stabile joining of the tread band itself. On the lateral surfaces of the carcass structure, each extending from one of the lateral edges of the tread band up to the respective annular anchoring structure to the beads, respective sidewalls made of elastomeric material are also applied.
By “component made of elastomeric material” of the tyre, it is intended any component of the tyre made of elastomeric material and not reinforced with wires or cords (e.g. tread band, sidewalls, liner, under-liner, fillers in the bead area, sidewall inserts in the self-supporting tyres, anti-abrasive inserts, etc.), or a portion thereof, or the set formed by two or more of the aforesaid components or portions thereof.
It must be specified that, with the term “elastomeric material” it is intended to indicate a composition comprising at least one elastomeric polymer and at least one reinforcement filler. Preferably, such composition further comprises additives such as, for example, a cross-linking agent and/or a plasticisation agent. Due to the presence of the cross-linking agent, through heating such material can be cross-linked, so as to form the final manufactured product.
By continuous surface relative to a forming drum, it is intended a surface without interruption or in which possible openings (such as holes or grooves) have size such that the elastomeric material of the semi-finished product that is rested thereon substantially does not penetrate them. The possible openings each have for example an area less than or equal to about 300 mm2 (e.g. groove with axial extension of about 150 mm for about 2 mm width) and the set of the openings overall have an area smaller than or equal to about 20%, preferably smaller than or equal to about 15% of the total area of said continuous surface.
The document WO 2008/099236, on behalf of the same Applicant, illustrates a process and an apparatus for manufacturing tyres in which a carcass sleeve is formed around an external surface of a forming drum, according to an application diameter greater than the fitting diameter of the tyre. For such purpose, one or more dispensers feed at least one continuous elongated element made of elastomeric material while the forming drum is rotated around its geometric axis, so as to form the liner on an external surface and on support surfaces of the forming drum. Application members sequentially apply a plurality of strip-like elements transversely arranged with respect to the circumferential extension of the external surface, while the forming drum is driven in rotation according to a step-by-step gait, in order to form a carcass ply. Around each of the end flaps of the carcass ply, an annular anchoring structure is coaxially engaged, defining the fitting diameter. An external sleeve comprising a belt structure associated with a tread band is arranged in a coaxially centred position around the carcass sleeve applied on the forming drum. The forming drum comprises a central section and two half-parts axially moveable with respect to the central section. Through mutual axial approaching of the two half-parts, the same carcass sleeve is shaped according to a toroidal configuration to determine the application thereof against a radially internal surface of the external sleeve, according to a “process of building in a single step” or “unistage process”.